1. Field of the Invention
The present invention relates to a heat sink element for decreasing the temperature of high-temperature portions of high-frequency electronic circuit substrates in electronic devices or wireless communication devices. More specifically, the present invention relates to a heat sink element which is directly connected to a high-potential printed wiring conductor having a circuit element connected thereto and decreasing the temperature by means on thermal conductivity. Furthermore, the present invention also relates to a high-frequency electronic circuit substrate using such heat sink element.
2. Description of the Related Art
A variety of heat sink means or cooling means have been employed in electronic devices or communication devices to suppress the increase in internal temperature caused by operation of the electronic devices or high-frequency signal operation of communication devices. For example, electric fans or heat sink plates have been used as such means. In the field of wireless communication devices, heat sink sheets such as silicon sheets were bonded to high-temperature parts, or circuit substrates were fixed to a metal case with a plurality of metal screws to remove heat in small radios.
With such conventional heat sink means or cooling means, in most cases, the heat of grounded conductors with a zero potential in internal electric or electronic circuits was withdrawn by direct thermal conductivity, whereas an indirect heat removal by convection of air created by a fan was used to decrease the temperature of high-potential zones (hot zones) in signal lines of circuits. However, miniaturization of devices, decrease in their weight, and reduction of cost placed a limitation on the heat withdrawal capacity of such indirect heat removal method and a demand arose for new heat sink means.
For example, in case of high-frequency electronic circuit substrates between antennas and transmission power amplifiers (abbreviated as PA hereinbelow) with a small size and a high output (e.g., 50W) in VHF-band radios (transceivers), or matched filter substrates such as LPF (low-pass filter) substrates with xcfx80-type two-stage configuration suppressing spurious emission, if a high-level high-frequency signal is applied to a capacitor and coil of the filter element, the power loss is 2-3 W even if the insertion loss is about 0.1 dB, and such power loss causes heat generation. Temperature increase due to such heat generation could exceed the quality assurance temperature (for example, 105xc2x0 C.) for printed substrates having a filter mounted thereon and a melting point (for example, about 180xc2x0 C.) of eutectic solders securing the coil or capacitor and reach about 200xc2x0 C., leading to degradation of substrate characteristics and separation of components.
FIG. 4 illustrates a circuit of a conventional xcfx80-type two-stage LPF. L1 and L2 are spiral coils obtained by winding a single wire with a diameter of about 1 mm to obtain an inner diameter of 3 mm. The number of turns in the coils is about 3t. Furthermore, C1, C2, C3 are ceramic capacitors with Q of about 150-200. Q-high capacitors may be used to decrease the insertion loss, but such capacitors increase the cost by a factor of 30-50. Moreover, 3a, 3b, 3c are high-potential printed wiring conductors.
The increase in temperature caused by heat generation in such matched filter substrates is the highest in the zone of series elements of a high-frequency signal line (high-potential side). The problem is, however, that all of the conventional heat sink means are practically ineffective for suppressing temperature increase at a high-potential side. Furthermore, the PA components are introduced into a metal package for heat removal, brought in flat surface contact with a case, and secured with a large number of screws. However, since the matched filter substrates serve as antenna connection circuits and have a miniaturized structure, they cannot be placed in the PA package. As a result, substrate characteristics are degraded and components are damaged due to a temperature increase. The only way to avoid such degradation is to decrease the transmission power, which becomes a weak point of transmitters.
Accordingly, a demand was created for heat sink elements capable of effectively decreasing the temperature of high-temperature components under a high potential in matched filter substrates or high-frequency electronic circuit substrates without using conventional heat removal means, and for circuits using such heat sink elements.
The heat sink element in accordance with the present invention is in the form of a coil obtained by spirally winding a wire with a high thermal conductivity, one end of the coil being directly connected to a high-potential circuit element connection conductor in a high-frequency circuit mounted on an electronic circuit substrate and the other end of the coil being directly secured to a metal case having the electronic circuit substrate contained therein, and serves as a heat channel for transferring the heat caused by temperature increase in the circuit element connection conductor to the metal case by means of thermal conductivity.
Another heat sink element in accordance with the present invention is in the form of a monolayer cylindrical coil obtained by spirally tightly winding a wire with a high thermal conductivity, one end of the monolayer cylindrical coil being directly connected to a high-potential circuit element connection conductor in a high-frequency circuit mounted on an electronic circuit substrate and the other end of the monolayer cylindrical coil being directly secured to a metal case having the electronic circuit substrate contained therein, and serves as a heat channel for transferring the heat caused by temperature increase in the circuit element connection conductor to the metal case by means of thermal conductivity. The inductance of the monolayer cylindrical coil determined by the coil radius and the number of turns is set such that it gives a sufficiently high impedance by comparison with the impedance at the operation signal frequency of the circuit element connection conductor portion to which one end of the monolayer cylindrical coil is connected, so as to produce no effect on characteristics of the high-frequency circuit.
Another heat sink element in accordance with the present invention is in the form of a monolayer cylindrical coil obtained by spirally tightly winding an insulator-coated copper wire, one end of the monolayer cylindrical coil being directly connected to a high-potential circuit element connection conductor in a high-frequency circuit mounted on an electronic circuit substrate and the other end of the monolayer cylindrical coil being directly secured to a metal case having the electronic circuit substrate contained therein, and serves as a heat channel for transferring the heat caused by temperature increase in the circuit element connection conductor to the metal case by thermal conductivity. The inductance of the monolayer cylindrical coil determined by the coil radius and the number of turns is set such that it gives a sufficiently high impedance by comparison with the impedance at the operation signal frequency of the circuit element connection conductor portion to which one end of the monolayer cylindrical coil is connected, so as to produce no effect on characteristics of the high-frequency circuit.
The high-frequency electronic circuit substrate in accordance with the present invention has a high-frequency circuit mounted thereon, is connected between an output terminal of a transmission power amplifier and an antenna, and is contained in a metal case, wherein heat channel means for transferring the heat caused by the temperature increase in a circuit element connection conductor which connects high-potential circuit elements of the high-frequency circuit to the metal case by thermal conductivity is provided between the circuit element connection conductor and the metal case. A heat sink element in the form of a coil obtained by spirally winding a wire with a high thermal conductivity and having one end thereof directly connected to the circuit element connection conductor and the other end thereof directly secured to the metal case, is used as heat channel means.
Furthermore, the high-frequency electronic circuit substrate in accordance with the present invention has a high-frequency circuit mounted thereon, is connected between an output terminal of a transmission power amplifier and an antenna, and is contained in a metal case, wherein heat channel means for transferring the heat caused by the temperature increase in a circuit element connection conductor which connects high-potential circuit elements of the high-frequency circuit to the metal case by thermal conductivity is provided between the circuit element connection conductor and the metal case. A heat sink element in the form of a monolayer cylindrical coil obtained by spirally tightly winding a wire with a high thermal conductivity, one end thereof being directly connected to the circuit element connection conductor and the other end thereof being directly secured to the metal case, is used as heat channel means. The inductance of the heat sink element is determined by the coil radius and the number of turns of the monolayer cylindrical coil. Thus, the inductance of the heat sink element is set such that it gives a sufficiently high impedance by comparison with the impedance at the operation signal frequency of the circuit element connection conductor portion to which one end of the monolayer cylindrical coil is connected, so as to produce no effect on characteristics of the high-frequency circuit.
Moreover, the high-frequency electronic circuit substrate in accordance with the present invention has a high-frequency circuit mounted thereon, is connected between an output terminal of a transmission power amplifier and an antenna, and is contained in a metal case, wherein heat channel means for transferring the heat caused by the temperature increase in a circuit element connection conductor which connects high-potential circuit elements of the high-frequency circuit to the metal case by thermal conductivity is provided between the circuit element connection conductor and the metal case. A heat sink element in the form of a monolayer cylindrical coil obtained by spirally tightly winding an insulator-coated copper wire, one end thereof being directly connected to the circuit element connection conductor and the other end being directly secured to the metal case, is used as heat channel means. Thus, the inductance of the heat sink element determined by the coil radius and the number of turns is set such that it gives a sufficiently high imedance by comparison with the impedance at the operation signal frequency of the circuit element connection conductor portion to which one end of the monolayer cylindrical coil is connected, so as to produce no effect on characteristics of the high-frequency circuit.